There has been traditionally proposed a biometrics authentication technology that identifies individuals on the basis of human physical features. For examples, fingerprints, hand geometry, retinas, faces, voices, and the like are used for biometrics authentication. Further, the irises of the human eyeballs have different characteristics depending on individuals. For example, Patent Literature 1 below therefore proposes an iris authentication system that uses the features of the irises.
The irises of all the human eyes have immensely complicated unique tissues, and it is known that the tissues are essentially invariable. The tissues or details of both irises of even the same person are not the same. The iris dilates and constricts to adjust the dimension of the pupil in response to light. The iris pattern slightly varies at this time, and this variation affects the accuracy of authentication in some cases. Further, Patent Literature 2 below discloses a method of generating an iris code for a method of analyzing such features of the iris. Specifically, an iris in a captured image is recognized, the inner border of the iris (circular border between the iris and the pupil) and the outer border of the iris are decided, and the circular iris is separated. A polar coordinate system is then set on the separated iris image. The origin of the coordinate system is placed at the center of the circular border between the iris and the pupil. Afterwards, the feature value of the iris image subjected to the polar coordinate conversion is extracted, and an iris code having a fixed length and a universal format for all irises is generated. The iris code generated in this way is stored as a reference code. At the time of authentication, an iris code similarly encoded is compared with the reference code stored in advance, and it is determined whether the iris code and the reference code originate from the same individual.
Further, using a pupil having the same size as that of the registered pupil at the time of iris authentication improves the authentication accuracy. Accordingly, Patent Literature 3 below proposes a system that varies the pupil of an eye in size by gently varying the intensity of illumination over time, and continuously captures eye images in which the pupil is different in size.
Further, in a case where an iris is imaged by adjusting the size of the pupil, the eye is illuminated for the adjustment as a general method. The illumination light is reflected by the cornea in front of the iris at this time, and overlaps with the iris image as a bright spot in some cases. If the bright spot appears in the image to hide part of the iris pattern, the authentication accuracy is adversely affected very much. It is then necessary to capture an image while preventing the reflected light of the illumination from hiding the iris. For example, Patent Literature 4 below has the imaging direction agree with the optical axis of the illumination, thereby preventing a bright spot from hiding the iris.